Broadband THz emission of long pulses from photomixing process with optical chirped pulses.

Terahertz (THz) generation via photomixing on photoconductive antenna using twin delayed chirped pulses provides a long THz pulse with a narrow bandwidth. To generate a long pulse with a broad bandwidth, we propose a new, to the best of our knowledge, method that combines two long optical pulses with opposite chirps. The pulses exhibit temporal distributions of their instantaneous frequencies with opposite slopes. As a result, the interaction between the time-evolving beat frequency and a photoconductor produces a broad THz spectrum with temporal variations. In our experimental setup, we generate a 12-ps-long pulse with a 1 THz bandwidth spectrum, featuring a frequency ramp of 90 GHz/ps, resembling a chirped THz pulse. By lowering optical peak power, this approach signifies a major advancement toward integrating photomixer technology, particularly in THz ranging applications.